1. Field of the Invention
The present invention relates to sound signal processing, and more particularly, to a sound signal processor and a method for processing a sound signal using the same, in which a sensed amplitude is used to prevent the generation of a plop noise when performing a sound mode checking operation.
2. Discussion of the Related Art
Television broadcast signals include separate audio and video components, i.e., a sound signal and a video signal. The sound signal contains sound system identification data for notifying a receiving system of transmission parameters, e.g., the sound carrier frequency, which may correspond to a broadcast for an M system or N system, a B system or G system, an I system, or a D system or K system, thereby necessitating reception based on MN, BG, I, or DK sound systems, respectively. Specific transmission parameters are typically set and transmitted by the broadcaster according to country or region but may vary according to transmission channel.
Meanwhile, a sound signal processor is provided to a video device such as a television receiver, which should be coordinated with the above transmission parameters. This coordination may be performed manually by referencing an guide for the television receiver's sound signal processor to save the sound mode settings, and multiple setup operations may be required for each of a given set of transmission channels. Therefore, a contemporary television receiver is provided with a function for automatic sound system setup, using a controller connected to a channel mode discriminator and a mode transition checker, to demodulate a sound intermediate frequency signal (hereinafter called a sound signal or SIF input) according to the appropriate sound system and a specific sound mode.
In the operation of such a sound signal processor, to which a sound signal as above is applied, the sound system is discriminated according to the sound system data provided in the broadcast signal. At the same time, according to the sound mode data, it is determined whether the currently applied sound signal, as determined by a currently broadcast signal, corresponds to a mono channel mode or to a stereo/dual channel mode, which may be one of several specific modes. That is, a continuous checking operation is performed with respect to the SIF input of the broadcast signal, to determine whether the sound signal as broadcast makes a transition from the mono channel mode to a specific stereo/dual channel mode. Thus, if a broadcast signal in the mono channel mode is received, a transition to the stereo/dual channel mode is detected, and once in the stereo/dual channel mode, it is continuously determined whether the current broadcast signal makes a further transition from a current stereo/dual channel mode to any one of its several specific sound modes. In other words, the mono channel mode (channel 1) consists of only one mode, but the stereo/dual channel mode (channel 2) consists of multiple modes.
FIG. 2 diagrams the above checking operation as executed by a contemporary sound signal processor. When a specific sound channel mode command is applied to the sound signal processor according to a broadcast channel, or when the video device is initially powered, if the received broadcast sound signal is in a mono channel mode 100, the continuous checking operation determines when, or whether, the mono channel mode makes a transition to a stereo/dual channel mode 101. In doing so, if the current sound channel mode corresponds to the mono channel mode 100, the controller (not shown) selects a sound system, namely, one of an MN system 102, a BG system 103, an I system 104, and a DK/K1/K2/K3 system 105, in accordance with the sound signal carrier frequency as set by the SIF input of the broadcast signal. Here, the sound signal of the MN system 102 has a carrier frequency of 4.5 MHz, that of the BG system 103 has a carrier frequency of 5.5 MHz, that of the I system 104 has a carrier frequency of 6.0 MHz, and that of the DK/K1/K2/K3 system 105 has a carrier frequency of 6.5 MHz, so that a filter value may be set for demodulation according to the corresponding sound system. The set filter value is also used in checking a specific sound mode of the sound signal.
Thereafter, once the current sound channel mode corresponds to the stereo/dual channel mode 101, a specific channel-2 sound mode of the selected sound system can be determined. For example, if the sound system corresponds to the MN system 102, it may be determined whether the current stereo/dual channel mode is a Zweiton mode 102a; if the sound system corresponds to the BG system 103, it may be determined whether the current stereo/dual channel mode is one of a near-instantaneously companded audio multiplex (NICAM) mode 103a or a Zweiton mode 103b; if the sound system corresponds to the I system 104, it may be determined whether the current stereo/dual channel mode is a NICAM mode 104a; and if the sound system corresponds to the DK/K1/K2/K3 system 105, it may be determined whether the current stereo/dual channel mode is a NICAM mode 105a or any one of three Zweiton modes 105b, 105c, and 105d. 
Notably, however, each of the BG and DK/K1/K2/K3 systems 103 and 105 includes multiple sound modes, such that, in the case of the selected sound system being either of the BG and DK systems, the continuous checking operation determines the current stereo/dual channel mode as being one of multiple possible sound modes. That is, it is possible that the stereo/dual channel mode transitions between the BG system modes 103a and 103b or among the DK/K1/K2/K3 system modes 105a-105d. 
Therefore, in a contemporary sound signal processor, while a broadcast signal in the mono channel mode is being received, the controller keeps checking whether the broadcast sound signal makes a transition to one of the stereo/dual channel modes. This sequentially performed operation of continuously checking for a sound mode transition produces an undesirable audio artifact, sometimes referred to as “plop noise,” which degrades the sound quality of a video device, e.g., a television receiver, adopting such a sound processor.